Talk:Sloped armour

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At thirty degrees to the horizontal the effect is about fifty percent.

Is that the equivalent of 50% thicker armour, 50% greater chance of deflection, 50% greater deflecting force? This needs an explanation and a reference source. —Michael Z. 2005-11-9 00:01 Z

None of the above. I just rewrote most of the article, but the last two paragraphs still need some work. Ergbert 19:48, 24 March 2006 (UTC)

Sorry, but the "fallacies" you removed are in fact correct. The increase of slope offers no direct weight advantage because of LOS increase. That is the common fallacy made :o).--MWAK 09:10, 23 June 2006 (UTC)

The article said nothing about protection at a given areal density -- it specifically referred to protection at a given normal thickness. Most of what you put in just isn't true, so I'm removing it again and clarifying what I wrote previously. Ergbert 03:44, 23 July 2006 (UTC)

Yes, the version you wrote had these defects :o). But I must admit that the present wording is much more precise. However, could you point out why you believe that the following points are untrue or shouldn't be explicitly mentioned:

1. There is a conceptual difference to be made between deflection in general and the special case of ricochet.
2. The shape of the penetrator and especially its length-diameter ratio influences the degree of deflection; older bullet-shaped rounds were more easily deflected.
3. Because the point of impact is also a friction point for bullet-shaped rounds the effect of "turning into the plate" negates deflection at angles below 45 degrees.
4. For bullet-shaped rounds the highest increment of deflection is around 67 degrees.
5. There is such an effect called the "back plate effect", a function of T-D ratio; for modern long-rod penetrators its easier to penetrate a plate at sixty degrees to the vertical than a vertical plate of the same area density, for the reason that the deformation of the penetrator leads to a different T-D ratio.
6. The reason why ceramic tiles benefit less from sloping is mainly their large face defeat component.
7. Modern tank design doesn't strive for deflection anymore simply because modern penetrators are difficult to deflect; for WWII tanks the benefits of deflection were the main reason to implement the principle of sloped armour, not the surface-volume ratio.

These, I think, are points so fundamental and generally accepted that it surprises me that anyone could consider them contentious. Could it also be that you have been focussed too much on modern developments? Deflection is unimportant for modern penetrators but was a major defeat mechanism in early WWII. --MWAK 06:54, 23 July 2006 (UTC)

1. What exactly do you mean by "deflection"? I have some texts on armor penetration from circa WWII and I don't recall them making that distinction (and if "deflection", as opposed to ricochet, was then the most important advantage of sloped armor (What about shattering of brittle penetrators? That's certainly mentioned.), I think they would've).
2. Shape and L:d ratio do affect ricochet, but the results for shape not only differ, but reverse, in different situations, and I did mention L:d ratio. There are also different sorts of bullet shapes.
3. "Increment of deflection" is something I have never encountered in all my reading on the subject...67 degrees is close to the ideal obliquity for deflecting WWII-era carbide-cored and APC shot (60-65 degrees), however, so maybe that's what you mean? AP shot is best defeated at only about 30 degrees obliquity, however.
4. The back plate/surface effect is why penetrators turn into the plate; it isn't responsible for the total destruction of armor.
5. Interface defeat seems to be pretty uncommon. Sloped ceramics are less effective at a given area density due to their earlier fracturing.
6. Sloped armor is still widely used today, and ricochet is still very much possible and likely a major reason for heavily sloped armor. Ergbert 04:09, 24 July 2006 (UTC)

I'll try to answer your points and (hopefully) make myself more clear:

1. Ricochet is a apecial case of deflection as a round doesn't have to "bounce off" the armour; even when it "gets stuck", it might still be deflected and this will affect penetration. Apart from problems in producing thick armour plates, the main reason to implement sloped armour was to benefit from deflection in general. You discuss the mathematical analysis first, but the article should first give the functional reason for the design concept and then give the mathematics — and mainly to point out there is no direct weight benefit, a mistake most people seem to make.
2. I agree, but it should be made explicit in the text that older penetrator shapes in general were much more prone to deflection, whereas for modern penetrators it's often easier to penetrate through armour that is sloped. See point four.
3. My wording was confusing. What I meant was that the derivative function peaks around 67 degrees. Between zero and 45 degrees the differential gains by increasing the slope are negligable, but then quickly start to increase. After 67 degrees (this is merely the theoretical optimum within a simplified model; actual numbers may vary) they again decline. This however does not mean that the ideal obliquity is to be found there, unless by "ideal" you mean: giving the ideal mix of deflection and surface-volume effects. After all, the shallower the angle, the better the deflection. That AP shot would be best defeated by thirty degrees armour is only true when the backplate effect is strongly relevant, i.e. with very large WWII rounds hitting armour that would, when sloped while keeping a given area density, be thinner than a quarter of the diameter of the round — or, if APDSFS is included in "AP" — with modern penetrators (at very long distances as their trajectory is so flat).
4. The backplate effect is often associated with 88 mm Tiger rounds punching out entire slabs of sloped T-34 armour that would have been able to resist them without it. Certainly the modern penetrator can't bring about such catastrophic failure. Nevertheless the main mechanism causing at sixty degrees a lesser protection than LOS thickness, is the backplate effect. This is counterintuitive. A round with such a small diameter simply shouldn't benefit from it. But when the tip of the penetrator bends upwards, this gives the same effect as a large diameter: it overloads the tensile strength of the remaining armour just the way a large round would, be it mainly in one axis. The rotation effects are secondary. Tate's article, though a classic, is very dated on this point.
5. Indeed I know of no ceramic able to effect a interface defeat against a large caliber penetrator :o). But even when penetration occurs, there has been a face defeat component of the total protection rendered, simply by the dwell caused by the surface resistance. And precisely because of the subsequent fracturing you mention, that feace defeat component is so important. We seem to refer to two aspects of one and the same effect and thus be in agreement ;o).
6. Well, ricochet with long rod penetrators is possible at only very shallow angles. Tate was even a tad optimistic. Only the Merkava seems to be designed with deflection in mind. That doesn't mean sloped armour isn't important any more — far from it. But it is used to deform and, above all, break the penetrator.--MWAK 14:03, 1 August 2006 (UTC)

"Back plate/surface effect", "interface defeat"? Sounds like this article and/or armor-piercing shot and shell need some work so the rest of us can read up and follow the conversation. —Michael Z. 2006-07-24 05:57 Z

I just created a short article on interface defeat. I hope it's long enough to be helpful. For the back surface effect, I'd prefer to find a good, reliable source that clearly defines it before I try to explain it. Ergbert 20:44, 24 July 2006 (UTC) Update: I added a mention of it to penetration (weapons). Ergbert 21:44, 24 July 2006 (UTC)

[edit] Picture

Nice picture Graeme!--MWAK 07:08, 28 June 2006 (UTC)

It came about it while playing with my son's wooden bricks - take two triangular ones slide them past each other and voila! GraemeLeggett 08:44, 28 June 2006 (UTC)